Extraretinal signals for congenital nystagmus.

Abstract

PURPOSE: Despite incessant to-and-fro oscillations of the eyes, persons with congenital nystagmus rarely report oscillopsia. This study evaluated the possibility that extraretinal signals of eye position are available to cancel the retinal image motion produced by nystagmus eye movements. METHODS: To assess the extraretinal signal for nystagmus, subjects pointed in the perceived direction of a target that was flashed for 2 msec in total darkness at various phases of the nystagmus waveform. RESULTS: All four subjects (two with jerk nystagmus and two with pendular nystagmus) made pointing errors that varied systematically according to what point in the nystagmus waveform the target was presented. In general, pointing errors varied in counterphase with changes in eye position, and amounted to approximately 25% of the nystagmus amplitude. CONCLUSION: These results indicate that extraretinal signals represent approximately 75% of the changes of eye position that occur in congenital nystagmus and therefore are potentially useful in preventing oscillopsia.